Temperature sensitive amorphous magnetic alloy

ABSTRACT

A detector is disclosed including a temperature sensitive amorphous magnetic alloy which shows a Curie point of not higher than 200° C. and whose composition is represented by the formula: 
     
         (M.sub.1-a Ni.sub.a).sub.100-z X.sub.z 
    
     wherein M=Co or Fe; X=at least one of P, B, C and Si; 0.2≦a≦0.8 when M is Co, or 0.4≦a≦0.9 when M is Fe; and 15≦z≦30.

This is a division of application Ser. No. 346,952, filed Feb. 8, 1982,now abandoned.

This invention relates to a temperature sensitive magnetic material, andmore particularly, relates to a temperature sensitive amorphous magneticalloy whose magnetic permeability varies abruptly in the vicinity of itsCurie point.

Conventionally, temperature sensitive magnetic materials have widelybeen used for a temperature sensor such as thermoswitch for a ricecooker, which may detect a preset temperature or protect a circuit byutilizing the property that a voltage, which is, for example, induced ata coil N_(L) by exciting a magnetic core 1 used as a heat sensor asshown in FIG. 1a, disappears at a temperature higher than the Curiepoint. (FIG. 1b illustrates a performance, in which t_(s) shows the timewhen the temperature of the magnetic core 1 has reached the Curiepoint). In general, the characteristics which are required of this kindof material should preferably be that the saturated magnetic fluxdensity is large, and the values of saturated magnetic flux density,coercive force and magnetic permeability relative to temperature varyabruptly at a preset temperature, and also that the heat response isquick. As the preset temperature, Curie point of the material is usuallyutilized. Therefore, it is preferable that a variety of Curie points isobtainable by varying the composition of the material.

Ferrites, having a Curie point of -40° C. to 150° C., has been used asthis kind of temperature sensitive material. However, ferrites have amagnetic flux density as low as 5,500 G, and its initial magneticpermeability in the vicinity of Curie point is at most about 7,000 at 10KHz, thereby showing small variation of the magnetic permeability at theCurie point. Ferrites are disadvantageous also in that they show slowheat response because of their poor thermal conductivity.

On the other hand, amorphous alloys which have no crystal structure havebeen noted because of their various interesting characteristics.Particularly, expected are applications thereof to novel soft magneticmaterials because they show excellent magnetic properties such as highersaturation magnetization, higher magnetic permeability and lowercoercive force. These amorphous alloys can be obtained by, for example,rapidly cooling molten mother alloys at a cooling rate of not less thanabout 10⁵ ° C./sec. Of the amorphous alloys, the one containing atransition metal such as iron(Fe) or cobalt(Co) as a main component anda metalloid element is known to have higher saturation magnetization andhigher magnetic permeability. Since, however, amorphous alloy is in ametastable condition, its characteristics generally vary by heating thealloy at a certain temperature which is considerably lower than itscrystallization temperature.

For example in the case of the above-mentioned amorphous alloys composedmainly of Fe or Co, crystallization gradually proceeds when it isexposed for a long time to a temperature higher than 300° C., with theresult that it becomes mechanically brittle and loses the tenacitypeculiar to amorphous alloys. Further, in the case of an amorphous alloyhaving a relatively higher Curie point, magnetic permeability isextremely lowered and coercive force increases even if it is heated at atemperature lower than 300° C., whereby the soft magnetic propertieswill deteriorate, and therefore such an amorphous alloy is not suitablefor a temperature-sensing element.

In view of the foregoing, this invention aims to provide a temperaturesensitive amorphous magnetic alloy whose magnetic flux density is largeand whose magnetic permeability varies markedly in the vicinity of itsCurie point, and which shows quick and sure response even when usedrepeatedly.

According to this invention, there is provided a temperature sensitiveamorphous magnetic alloy which shows a Curie point of not higher than200° C. and whose composition is represented by the formula:

    (M.sub.1-a Ni.sub.a).sub.100-z X.sub.z

wherein M represents a cobalt atom(Co) or an iron atom(Fe); X representsat least one of a phosphorus atom(P), a boron atom(B), a carbon atom(C)and a silicon atom(Si); a is a numeral ranging between 0.2 and 0.8inclusive (i.e., 0.2≦a≦0.8), preferably between 0.5 and 0.7 inclusive(i.e., 0.5≦a0.7) when M is Co, or a is a numeral ranging between 0.4 and0.9 inclusive (i.e., 0.4≦a≦0.9), preferably between 0.6 and 0.8inclusive (i.e., 0.6≦a≦0.8) when M is Fe; and z is a numeral rangingbetween 15 and 30 inclusive (i.e., 15≦z≦30), preferably between 20 and25 inclusive (i.e., 20≦z≦25).

In the above formula, when the component represented by M (i.e., Co orFe) is substituted with not more than 5 atom %, relative to the totalformula weight (excluding X), of chromium (Cr), i.e, where M+Ni=1.0, themagnetic permeability of the alloy is enhanced and the change of themagnetic permeability in the vicinity of the Curie point becomes moreremarkable.

This invention is based on the finding that an amorphous alloy having nocrystal structure and being in a metastable condition changes itscharacteristics when heated up to a temperature around a specific point(i.e., Curie point). It has been found particularly that the amorphousalloy according to this invention changes sharply its magneticpermeability in the vicinity of the Curie point, and further that it hasthe temperature sensitivity such that it shows quick and sure responseeven when used repeatedly.

Nickel(Ni) used in the alloy according to this invention is an elementeffective for adjusting the response temperature, i.e., the Curie pointof the alloy. When it is used in combination with Co in such an amountthat the numeral a in the above formula is less than 0.2 (i.e., a≦0.2),the Curie point of the alloy will become higher than 200° C. and thethermal stability of the alloy will be inferior after repeated usethereof and the change of the magnetic permeability of the alloy in thevicinity of the Curie point will be too large for the alloy to bepractically applied. If Ni is employed in such an amount that thenumeral a is larger than 0.8 (i.e., a≧0.8), the Curie point of the alloywill become lower than the liquid nitrogen temperature, which rendersthe alloy impractical in applications.

When Ni is used in combination with Fe in such an amount that thenumeral a is less than 0.4 (i.e., a≦0.4), the Curie point will becomehigher than 200° C. and the thermal stability of the alloy will beinferior after repeated use thereof and the change of the magneticpermeability of the alloy in the vicinity of the Curie point will be toolarge for the alloy to be practically applied. If Ni is employed in suchan amount that the numeral a is larger than 0.8 (i.e., a≧0.8), the Curiepoint will become lower than liquid nitrogen temperature, which rendersthe alloy impractical in applications.

Chromium(Cr) is an element effective for enhancing the magneticpermeability of the alloy, improving the corrosion resistance of thealloy and also adjusting the Curie point of the alloy. However, if itscontent exceeds 5 atom % with respect to Fe or Co, the preparation ofamorphous alloy will become more difficult.

The X is an element or elements essential for making the alloyamorphous. If, however, the amount thereof is out of those defined inthis invention, the formation of amorphous alloy will become difficult.

This invention will be described below in more detail by way ofExamples, and with reference to the accompanying drawings, in which;

FIG. 1, already referred to in the foregoing, is a view illustrating aprinciple for a construction example where a temperature sensitivemagnetic material is employed for a magnetic core (1) to performtemperature control;

FIGS. 2 and 4 are graphical representations showing the Curie point ofthe alloy depending upon the content of Ni; and

FIGS. 3 and 5 are graphical representations showing the change inmagnetic permeability depending upon the temperature.

EXAMPLE 1

Prepared by twin-roller method were amorphous alloys having acomposition of (Co_(1-a) Ni_(a))₇₅ Si₁₀ B₁₅, each having thickness of 30μm. These were partially cut out and annealed at 400° C. for tenminutes. Thereafter, temperature valiations of their magnetization weremeasured by the use of a vibrating sample magnetometer (VSM) to obtainCurie points Tc. Relationship between Tc and the content of Ni are shownin FIG. 2, from which it will be seen that Curie point decreasesmonotonously with Ni contents.

Measured next were temperature variations of effective permeability at10 KHz, i.e., μ'_(10k), with respect to every composition given in FIG.2. Results are shown in FIG. 3 as to a representative example, (Co₀.35Ni₀.65)₇₈ Si₈ B₁₄. It can be seen therefrom that the magneticpermeability in the vicinity of Tc (5° C.) indicates 80,000 which is farlarger than 7,000 in the case of ferrites, and also that the differencebetween the temperature providing maximum value of μ'_(10k) and thetemperature of Tc is as small as 3° C. and an abrupt variation ofpermeability takes place by such a slight temperature-difference.

A heat cycle ranging from room temperature to the Curie point (5° C.)was repeated a hundred times in respect of the above same sample, butdeterioration of magnetic permeability and variation with time of theCurie point were not observed and good thermal stability was recognizedthereabout.

The same heat cycle as above was repeated also for each of the amorphousalloys having various Ni contents shown in FIG. 2 to observe thevariations of magnetic permeabilities and Curie points. It was therebyconfirmed that the amorphous alloys outside this invention caused thevariation of Curie point and the deterioration of magnetic permeabilitywhen the heat cycle was repeated several times, and therefore were notsuitable for temperature sensitive magnetic materials.

EXAMPLE 2

Prepared by twin-roller method were amorphous alloys having acomposition of (Fe_(1-a) Ni_(a))₇₅ B₂₅, each having thickness of 30 μm.These were subjected to heat treatment at 400° C. for fifteen minutes,and thereafter, dependence of Tc for Ni content was determined to obtainthe results as shown in FIG. 4. Measured was μ'_(10k) with respect toevery composition given in FIG. 4. Results are shown in FIG. 5 as to arepresentative example, (Fe₀.25 Ni₀.75)₈₀ B₂₀. It can be seen therefromthat the μ'_(10k) in the vicinity of Tc (75° C.) indicates 20,000 whichis far larger than 7,000 in the case of ferrites.

A heat cycle ranging from room temperature to Tc (75° C.) was repeated ahundred times in respect of the above same sample, but deterioration ofmagnetic permeability and variation of the Curie point were not observedand good thermal stability was recognized thereabout.

Similarly, the heat cycle ranging from room temperature to Tc wasrepeated for each of the amorphous alloys having various Ni contentsshown in FIG. 4 to observe the variations of magnetic permeabilities andCurie points. It was thereby found that the amorphous alloys outsidethis invention caused the variation of Tc with time and thedeterioration of magnetic permeability when the heat cycle was repeatedseveral times, and therefore were not suitable for temperature sensitivemagnetic materials.

EXAMPLES 3 TO 16 AND COMPARATIVE EXAMPLES 1 TO 5

Prepared by twin-roller method and annealed at 400° C. for 10 to 15minutes were amorphous alloys as shown in Table 1, for which the Tc andthe values of μ'_(10k) in the vicinity of Tc were determined in the samemanner as in Example 1. Results are shown together in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                               Maximum value                                                                 of μ'.sub.10k in the                                   Composition   Tc (°C.)                                                                     vicinity of Tc                                                                        ΔT*                                  __________________________________________________________________________    Example 3                                                                            (Co.sub.0.3 Ni.sub.0.7).sub.80 Si.sub.10 B.sub.10                                           7     85,000  3                                          Example 4                                                                            (Co.sub.0.3 Ni.sub.0.7).sub.80 P.sub.14 B.sub.6                                             -3    64,000  3                                          Example 5                                                                            (Co.sub.0.3 Ni.sub.0.7).sub.80 P.sub.16 B.sub.1 C.sub.3                                     -11   62,000  3                                          Comparative                                                                          (Co.sub.0.1 Ni.sub.0.9).sub.79 Si.sub.8 B.sub.13                                            -135  12,000  10                                         Example 1                                                                     Example 6                                                                            (Co.sub.0.2 Ni.sub.0.8).sub.79 Si.sub.8 B.sub.13                                            -95   43,000  5                                          Example 7                                                                            (Co.sub.0.5 Ni.sub.0.5).sub.79 Si.sub.8 B.sub.13                                            190   51,000  3                                          Example 8                                                                            (Co.sub.0.8 Ni.sub.0.2).sub.75 Si.sub.10 B.sub.15                                           170   22,000  5                                          Comparative                                                                          (Co.sub.0.9 Ni.sub.0.1).sub.79 Si.sub.8 B.sub.13                                            440   10,000  9                                          Example 2                                                                     Example 9                                                                            (Co.sub.0.3 Ni.sub.0.67 Cr.sub.0.03).sub.78 Si.sub.8 B.sub.14                               -35   110,000 2                                          Example 10                                                                           (Co.sub.0.3 Ni.sub.0.66 Cr.sub.0.04).sub.78 Si.sub.8 B.sub.14                               - 50  58,000  3                                          Comparative                                                                          (Co.sub.0.3 Ni.sub.0.61 Cr.sub.0.09).sub.78 Si.sub.8 B.sub.14                               -125  15,000  15                                         Example 3                                                                     Example 11                                                                           (Fe.sub.0.3 Ni.sub.0.7).sub.78 P.sub.10 B.sub.12                                            -43   18,000  4                                          Example 12                                                                           (Fe.sub.0.3 Ni.sub.0.5).sub.74 Si.sub.10 B.sub.16                                           180   14,000  5                                          Example 13                                                                           (Fe.sub.0.6 Ni.sub.0.4).sub.72 Si.sub.10 B.sub.18                                           160   11,000  6                                          Example 14                                                                           (Fe.sub.0.1 Ni.sub.0.9).sub.78 Si.sub.8 B.sub.14                                            -60    7,000  7                                          Comparative                                                                          (Fe.sub.0.7 Ni.sub.0.2).sub.78 Si.sub.8 B.sub.14                                            440    2,000  12                                         Example 4                                                                     Example 15                                                                           (Fe.sub.0.3 Ni.sub.0.67 Cr.sub.0.03).sub.78 Si.sub.8 B.sub.14                               -48   25,000  3                                          Example 16                                                                           (Fe.sub.0.3 Ni.sub.0.66 Cr.sub.0.04).sub.78 Si.sub.8 B.sub.14                               -65   25,000  3                                          Comparative                                                                          (Fe.sub.0.3 Ni.sub.0.61 Cr.sub.0.09).sub.78 Si.sub.8 B.sub.14                               -140  11,000  15                                         Example 5                                                                            Mn--Zn Ferrites                                                                             120    6,000  10                                         __________________________________________________________________________     *ΔT: Temperaturedifference between the temperature showing maximum      value of μ'.sub.10k and the temperature of Curie point.               

The μ'_(10k) value and Tc were measured after the heat cycle rangingfrom room temperature to Tc. As the results, no variation of Tc withtime and no deterioration of μ'_(10k) were virtually recognized aboutamorphous alloys having the composition which may render the Tc lowerthan 200° C., namely, the amorphous alloys of, for instance, a≧0.2 inthe case of Example 1 and a≧0.4 in the case of Example 2.

As explained above, the temperature sensitive amorphous alloy accordingto this invention has excellent temperature sensitive characteristicssuch that it shows large temperature-variation of magnetic permeabilityin the vicinity of its Curie point; it can vary the magneticpermeability abruptly because of its narrow ΔT, and it has higherthermal conductivity and quick heat-response since it is of a metallicmaterial and yet of a thin plate; it is possible to easily adjust theCurie point and optionally change the preset temperature to atemperature lower than 200° C. by varying its composition, particularly,the Ni content. Thus, it is a temperature sensitive magnetic materialindustrially advantageous as a temperature sensor.

This temperature sensitive magnetic material may be used as a toroidalcore as shown in FIG. 1, or a long and linear material may be used assuch for a temperature sensor.

We claim:
 1. A method for detecting a predetermined temperature,comprising the steps of:(a) by electromagnetically exciting a magneticcore element, inducing a voltage in electrically conductive means, whichcore element is comprised of a temperature sensitive amorphous magneticalloy having a Curie point at approximately said predeterminedtemperature, which Curie point is not higher than 200° C., said alloyconsisting essentially of a composition represented by the formula

    (M.sub.1-a-b Ni.sub.a Cr.sub.b).sub.100-z X.sub.z

wherein M represents a cobalt atom or an iron atom; X represents atleast one of a phorophorous atom, a boron atom, a carbon atom and asilicon atom; a is a numeral ranging between 0.2 and 0.8 inclusive whenM is Co, or a is a numeral ranging between 0.4 and 0.9 inclusive when Mis Fe; b is a numeral ranging between 0 and 0.05, such that the sum of aand b does not exceed 0.8 when M is cobalt or 0.9 when M is iron; and zis a numeral ranging between 15 and 30 inclusive, and wherein a and zare selected such that the temperature difference between thetemperature showing the maximum value of effective permeability at 10kHz and the temperature of the Curie point is less than 10 centigradedegrees; (b) heating said core to a temperature above said predeterminedtemperature; and then (c) measuring an abrupt decrease in said voltage.2. A temperature-activated switch device, comprising (1) a magnetic corewhich has a magnetic permeability that varies markedly at apredetermined temperature, and (2) means for exciting said core in orderto produce an induced voltage, wherein said core comprises a temperaturesensitive amorphous magnetic alloy having a Curie point at approximatelysaid predetermined temperature, which Curie point is not higher than200° C., said alloy consisting essentially of a composition representedby the formula

    M.sub.1-a-b Ni.sub.a Cr.sub.b).sub.100-z X.sub.z

wherein M represents a cobalt atom or an iron atom; X represents atleast one of a phosphorus atom, a boron atom, a carbon atom and asilicon atom; a is a numeral ranging between 0.2 and 0.8 inclusive whenM is Co, or a is a numeral ranging between 0.4 and 0.9 inclusive when Mis Fe; b is a numeral ranging between 0 and 0.05, such that the sum of aand b does not exceed 0.8 when M is cobalt or 0.9 when M is iron; and zis a numeral ranging between 15 and 30 inclusive, and wherein a and zare selected such that the temperature difference between thetemperature showing the maximum value of effective permeability at 10kHz and the temperature of the Curie point is less than 10 centigradedegrees.
 3. A temperature-activated switch device according to claim 2,wherein M is Co.
 4. A temperature-activated switch device according toclaim 3, wherein b is
 0. 5. A temperature-activated switch deviceaccording to claim 4, wherein a is between 0.5 and 0.7 inclusive and xis between 20 and 25 inclusive.
 6. A temperature-activated switch deviceaccording to claim 2, wherein M is Fe.
 7. A temperature-activated switchdevice according to claim 6, wherein b is
 0. 8. A temperature-activatedswitch device according to claim 7, wherein a is between 0.6 and 0.8inclusive and z is between 20 and 25 inclusive.